This invention relates to an improved solder interconnection for mounting an electronic component onto a printed circuit board. More particularly, this invention relates to a solder interconnection comprising an interwoven copper fiber mat to enhance compliancy for resisting stresses due to thermal cycling without sacrifice to thermal and electrical conductivity required of the interconnection.
A typical electronic device comprises a component mounted onto a printed circuit board by a solder connection. For example, a power amplifier comprises a load resistor element soldered to the printed circuit board. The resistor is based upon a ceramic block that carries a resistive film, whereas the printed circuit board is formed of glass fiber-reinforced epoxy polymer. The solder joint extends between electroplated copper leads on the resistor element and also on the circuit board to electrically connect the resistive film to the circuit on the board. During operation, the resistor element generates heat, a portion of which is dissipated through the solder joint. In addition, this thermal cycling is accompanied by expansion and contraction of the element and the board, but at different rates due to the difference in the thermal expansion coefficients of the materials. This differential thermal expansion generates lateral stresses within the solder joint, which in turn may lead to breakage of the joint and failure of the circuit. Furthermore, the solder alloy used for the joints exhibit undesirably high electrical resistance and low thermal conductivity, particularly in comparison to preferred electrical circuit metals such as copper. Thus, it is desired to minimize the distance through the solder to minimize resistive current loss that would otherwise generate unwanted heat at the joint. It is also desired to minimize the solder gap between the copper leads to promote heat dissipation from the component.
Therefore, there has been a long standing need for a solder connection betwen a surface mounted electrical component and a substrate that has enhanced compliance to withstand stresses due to differential thermal expansion of the materials thereof, while minimizing the electrical and thermal conductive path through the solder that would otherwise retard electrical current flow and inhibit heat dissipation.